Three-dimensional memory devices and methods for forming the same

ABSTRACT

Embodiments of three-dimensional (3D) memory devices and methods for forming the 3D memory devices are disclosed. In an example, a NAND memory device includes a substrate, one or more peripheral devices on the substrate, a plurality of NAND strings above the peripheral devices, a single crystalline silicon layer above and in contact with the NAND strings, and interconnect layers formed between the peripheral devices and the NAND strings. In some embodiments, the NAND memory device includes a bonding interface at which an array interconnect layer contacts a peripheral interconnect layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/047,251, filed on Jul. 27, 2018 and titled “Three-Dimensional MemoryDevices and Methods For Forming The Same,” now U.S. Pat. No. 11,211,397issued on Dec. 28, 2021, which claims priority to InternationalApplication No. PCT/CN2018/077750, filed Mar. 1, 2018, which claimspriority to Chinese Patent Application No. 201710716657.1 filed on Aug.21, 2017 and Chinese Patent Application No. 201710716640.6 filed on Aug.21, 2017, all of which are incorporated herein by reference in theirentireties.

BACKGROUND

Embodiments of the present disclosure relate to three-dimensional (3D)memory devices and fabrication methods thereof.

Planar memory cells are scaled to smaller sizes by improving processtechnology, circuit design, programming algorithms, and fabricationprocess. However, as feature sizes of the memory cells approach a lowerlimit, planar process and fabrication techniques become challenging andcostly. As a result, memory density for planar memory cells approachesan upper limit.

A 3D memory architecture can address the density limitation in planarmemory cells. The 3D memory architecture includes a memory array andperipheral devices for controlling signals to and from the memory array.

BRIEF SUMMARY

Embodiments of 3D memory architectures and fabrication methods thereofare disclosed herein.

In some embodiments, a semiconductor apparatus includes a siliconsubstrate with a peripheral device on the silicon substrate and one ormore interconnect layers above the peripheral device. The semiconductorapparatus can also include a memory array (also referred to herein as an“array device”) above the one or more interconnect layers. In someembodiments, the semiconductor apparatus includes a single crystallinesilicon layer at an upper end of the array device. The semiconductorapparatus can further include a plurality of back-end-of-line (BEOL)interconnect layers and pad layers above the single crystalline siliconlayer.

In some embodiments, the peripheral device includes a plurality ofmetal-oxide-semiconductor (MOS) field-effect-transistors (FETs). Theperipheral device can be formed on a silicon substrate, which includesone or more doped regions and isolation regions. The MOSFETs of theperipheral device can provide different functions for the semiconductorapparatus such as page buffer, sense amplifier, column decoder, and rowdecoder functions.

In some embodiments, the one or more interconnect layers include aperipheral interconnect layer, which includes a plurality of conductorlayers and contact layers. The conductor layers can include a pluralityof metal layers, in which one or more of the metal layers can includetungsten (W), copper (Cu), aluminum (Al), or any other suitablematerials. The contact layers can also include W, Cu, Al, or any othersuitable materials. The peripheral interconnect layer can transferelectrical signals between different peripheral transistors and betweenthe peripheral device and the array device.

In some embodiments, the one or more interconnect layers also include anarray interconnect layer, which includes a plurality of conductor layersand contact layers. The conductor layers can include a plurality ofmetal layers, in which one or more of the metal layers can include W,Cu, Al, or any other suitable materials. The contact layers can alsoinclude W, Cu, Al, or any other suitable materials. The arrayinterconnect layer can transfer electrical signals between differentareas of the array device and between the peripheral device and thearray device.

In some embodiments, the array device includes a plurality of NANDstrings. The array device can further include a plurality ofinterconnect layers below the NAND strings. Further, the singlecrystalline silicon layer can be above and contact the NAND strings. Insome embodiments, the single crystalline silicon layer is part of asilicon substrate that has been thinned by any suitable techniques, suchas backside grinding, wet/dry etching, and/or chemical mechanicalpolishing (CMP). The single crystalline silicon layer can have athickness between 200 nm and 50 μm, between 500 nm and 10 μm, or between500 nm and 5 μm. In some embodiments, the single crystalline siliconlayer has a thickness less than about 1 μm. In some embodiments, thesingle crystalline silicon layer is partially or fully doped with n-typeand/or p-type dopants.

In some embodiments, a NAND string includes a semiconductor channel(e.g., a silicon channel) that extends vertically through a pluralityconductor/dielectric layer pairs. The plurality of conductor/dielectriclayer pairs are also referred to herein as an “alternatingconductor/dielectric stack.” The conductor layer of the alternatingconductor/dielectric stack can be used as a word line (electricallyconnecting one or more control gates). Multiple layers can be formedbetween the conductor layer (control gate) of the alternatingconductor/dielectric stack and the semiconductor channel. In someembodiments, the multiple layers include a tunneling layer, such as atunneling oxide layer, through which the electrons or holes from thesemiconductor channel can tunnel to a storage layer of the NAND string.The multiple layers can also include a storage layer (also known as“charge trap/storage layer”) to store charge. The storage or removal ofcharge in the storage layer can impact the on/off state and/or aconductance of the semiconductor channel. The storage layer can includepolycrystalline silicon (polysilicon) or silicon nitride. In someembodiments, the multiple layers further include a blocking layer, suchas a silicon oxide layer or a combination of silicon oxide/siliconnitride/silicon oxide (ONO) layers. In some embodiments, the blockinglayer includes high dielectric constant (high-k) dielectrics (e.g.,aluminum oxide).

In some embodiments, the NAND string further includes an epitaxialsilicon layer on an upper end of the semiconductor channel. Theepitaxial silicon layer can be epitaxially grown from the singlecrystalline silicon layer.

In some embodiments, the NAND string further includes a select gateformed by one or more upper conductor layers of the alternatingconductor/dielectric stack. The select gate can control the on/off statstate us and/or a conductance of the semiconductor channel of the NANDstring. The select gate of the NAND string can also be formed by aseparate conductor layer above the alternating conductor/dielectricstack. In some embodiments, the NAND string further includes a selectgate formed by one or more lower conductor layers of the alternatingconductor/dielectric stack. The select gate of the NAND string can alsobe formed by a separate conductor layer below the alternatingconductor/dielectric stack.

In some embodiments, the NAND string is electrically connected to asource contact by a doped region of the single crystalline silicon layerabove the NAND string. The doped region of the single crystallinesilicon layer can include p-type dopants. The source contact can extendvertically through the alternating conductor/dielectric stack and cancontact the single crystalline silicon layer on its upper end. In someembodiments, a lower end of the source contact is in contact with acontact below the source contact.

In some embodiments, the array device further includes a plurality ofword line contacts, which extend vertically. Each of the plurality ofword line contacts can include an upper end in contact with acorresponding word line to individually address the corresponding wordline of the array device. The plurality of word line contacts can becontact holes and/or contact trenches (e.g., formed by a wet etchprocess or a dry etch process) filled with a conductor (e.g., W). Insome embodiments, the contact holes and contact trenches include abarrier layer, an adhesion layer, and/or a seed layer underneath theconductor. The contact holes and/or contact trenches can be filled by achemical vapor deposition (CVD) process, a physical vapor deposition(PVD) process, or an atomic layer deposition (ALD) process.

In some embodiments, the interconnect layers below the NAND stringsinclude a plurality of bit line contacts each in contact with a lowerend of a corresponding NAND string. The plurality of bit line contactscan include contact vias that are isolated from each other. Each bitline contact can be electrically connected to a corresponding NANDstring to individually address the corresponding NAND string. The bitline contacts can be contact holes and/or contact trenches (e.g., formedby a wet etch process or a dry etch process) filled with a conductor(e.g., W). The contact holes and/or contact trenches can be filled by aCVD process, a PVD process, or an ALD process. In some embodiments, thebit line contacts are initially formed above the NAND strings, followedby a wafer flipping process that flips the structure upside down so thatthe bit line contacts are positioned below the NAND strings in thesemiconductor apparatus.

In some embodiments, the one or more interconnect layers further includea bonding interface between two dielectric layers, such as between asilicon nitride layer and a silicon oxide layer. The bonding interfacecan also be between two conductor layers, such as between two metal(e.g., Cu) layers. In some embodiments, the bonding interface includesboth the interface between dielectric layers and the interface betweenconductor layers. The bonding interface can be formed by chemical bondsbetween the dielectric layers and/or the conductor layers on both sidesof the bonding interface. The bonding interface can be formed byphysical interaction (e.g., inter-diffusion) between the dielectriclayers and/or the conductor layers on both sides of the bondinginterface. In some embodiments, the bonding interface is formed after aplasma treatment or a thermal treatment of the surfaces on both sides ofthe bonding interface prior to the bonding process.

In some embodiments, the semiconductor apparatus further includesmultiple alternating conductor/dielectric stacks. In some embodiments,an inter-stack layer is between adjacent alternatingconductor/dielectric stacks. The inter-stack layer can electricallyconnect a NAND string from an upper alternating conductor/dielectricstack to another NAND string from a lower alternatingconductor/dielectric stack. In some embodiments, a NAND string from theupper alternating conductor/dielectric stack is electrically connectedto a NAND string from the lower alternating conductor/dielectric stackvia a conductor of the inter-stack layer, thereby creating a longer NANDstring.

In some embodiments, the semiconductor apparatus further includes aplurality of through array contacts (TACs) that extend verticallythrough the alternating conductor/dielectric stack(s). The plurality ofTACs are in contact with an interconnect layer (e.g., the arrayinterconnect layer) below the alternating conductor/dielectric stack andalso in contact with another interconnect layer (e.g., the BEOLinterconnect layer) above the alternating conductor/dielectric stack.The TACs can be contact holes and/or contact trenches (e.g., formed by awet etch process or a dry etch process) filled with a conductor (e.g.,W, Cu, or silicides).

In some embodiments, the BEOL interconnect layer transfers electricalsignals between devices of the semiconductor apparatus, including thearray device and the peripheral device. In some embodiments, pad layersare formed to transfer electrical signals from the semiconductorapparatus to external electrical signal paths. The BEOL interconnectlayer can include conductor layers and contact layers. The conductorlayers and contact layers can include conductor materials, such as W,Cu, Al, silicides, and/or any other suitable conductor materials. Thepad layers can also include conductor materials, such as W, Cu, Al,silicides, or any other suitable conductor materials.

An exemplary method for fabricating a semiconductor apparatus includesforming a peripheral device, forming an array device, and bonding theperipheral device to the array device at a bonding interface. The methodfurther includes forming the peripheral device, including MOStransistors, on a first silicon substrate, and forming a peripheralinterconnect layer above the peripheral device.

In some embodiments, the exemplary method further includes forming oneor more doped regions and isolation regions in a second siliconsubstrate, and forming one or more NAND strings on the second siliconsubstrate. The NAND strings include a plurality of conductor/dielectriclayer pairs, a semiconductor channel that extends vertically through theplurality of conductor/dielectric layer pairs, a tunneling layer betweenthe semiconductor channel and the conductor/dielectric layer pairs, astorage layer including a plurality of storage units between thetunneling layer and the conductor/dielectric layer pairs, a blockinglayer between the storage layer and the conductor/dielectric layerpairs, and an epitaxial single crystalline silicon layer (epitaxialplug) formed on an end of the semiconductor channel. The NAND stringscan contact the second silicon substrate. The epitaxial singlecrystalline silicon layer can be epitaxially grown from the secondsilicon substrate. Each NAND string can include a select gate at an endof the NAND string.

In some embodiments, the exemplary method further includes forming anarray interconnect layer above the NAND strings. The array interconnectlayer can include bit line contacts in contact with the NAND strings.The array interconnect layer can also include one or more conductorlayers and contact layers, each of which includes conductor materials,such as W, Al, Cu, or any other suitable conductor materials.

The array interconnect layer further includes a source contact for theNAND strings, according to some embodiments. The source contact canextend vertically through the alternating conductor/dielectric stack.The source contact can contact the second silicon substrate at an endand contact the array interconnect layer on another end. In someembodiments, the source contact is electrically connected to the NANDstrings by the second silicon substrate.

The peripheral device can be bonded to the array device by flipping thearray device upside down, aligning the array interconnect layer facingdown to the peripheral device with the peripheral interconnect layerfacing up (in a face-to-face manner), placing the array device above theperipheral device so that the array interconnect layer is above and incontact with the peripheral interconnect layer, performing a bondingtreatment, and forming a bonding interface between the arrayinterconnect layer and the peripheral interconnect layer. In someembodiments, the bonding treatment includes a plasma process, a wetprocess, and/or a thermal process to create physical and/or chemicalbonds between the array interconnect layer and the peripheralinterconnect layer at the bonding interface. In some embodiments, thearray interconnect layer includes silicon nitride layer or a siliconoxide layer, and the peripheral interconnect layer includes a siliconoxide layer or a silicon nitride layer. In some embodiments, theconductors of the array interconnect layer and the peripheralinterconnect layer include Cu.

In some embodiments, the bonding between the array interconnect layerand the peripheral interconnect layer is formed by physical interaction(e.g., inter-diffusion) between the dielectric layers (e.g., a siliconnitride layer and a silicon oxide layer) and/or the conductor layers atan interface. The interface between the array interconnect layer and theperipheral interconnect layer is referred to herein as a “bondinginterface.” In some embodiments, before the bonding process, a plasmatreatment on surfaces of the array interconnect layer and the peripheralinterconnect layer is performed to enhance the bonding strength betweenthe surfaces. Prior to the bonding process, a wet process treatment onthe surfaces of the array interconnect layer and the peripheralinterconnect layer can be performed as well to enhance the bondingstrength. In some embodiments, placement of the array interconnect layerabove the peripheral interconnect layer includes aligning contact areasof the array interconnect layer and the peripheral interconnect layer toensure electrical contact when the two interconnect layers are bonded.In some embodiments, after the interconnect layers have been madecontact with one another, a thermal treatment is performed to boostinter-diffusion between the conductor materials (e.g., Cu) of the arrayinterconnect layer and the peripheral interconnect layer.

In some embodiments, one or more bonding interfaces can be formed by thefabrication process. For example, multiple array devices can be bondedwith the peripheral device. In another example, the array device can bebonded with multiple peripheral devices. In still another example,multiple array devices can be bonded with multiple peripheral devices.

The exemplary method can further include forming more than onealternating conductor/dielectric stack. Each alternatingconductor/dielectric stack can include a plurality ofconductor/dielectric layer pairs. In some embodiments, an inter-stacklayer is formed between adjacent alternating conductor/dielectricstacks. The inter-stack layer can electrically connect a NAND stringextending vertically through an upper alternating conductor/dielectricstack to another NAND string extending vertically through a loweralternating conductor/dielectric stack.

The exemplary method can further include, after bonding the array deviceand the peripheral device, thinning the second silicon substrate of thearray device. The thinning of the second silicon substrate can beperformed by a CMP process, a wet etch process, a dry etch process, orany combination thereof.

In some embodiments, the order of forming the array device/arrayinterconnect layer and the peripheral device/peripheral interconnectlayer can be modified, or the fabrication of the array device/arrayinterconnect layer and the fabrication of the peripheraldevice/peripheral interconnect layer can be performed in parallel.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate embodiments of the present disclosureand, together with the description, further serve to explain theprinciples of the present disclosure and to enable a person skilled inthe pertinent art to make and use the present disclosure.

FIG. 1 illustrates a cross-section of an exemplary 3D memory device.

FIG. 2 illustrates a cross-section of a 3D memory device, according tosome embodiments.

FIGS. 3A-3D illustrate an exemplary fabrication process for forming aperipheral device and a peripheral interconnect layer, according to someembodiments.

FIGS. 4A-4D illustrate an exemplary fabrication process for forming anarray device and an array interconnect layer, according to someembodiments.

FIGS. 5A-5C illustrate an exemplary fabrication process for forming a 3Dmemory device with an array device bonded to a peripheral device,according to some embodiments.

FIG. 6 is a flowchart of an exemplary method for forming a peripheraldevice and a peripheral interconnect layer, according to someembodiments.

FIG. 7 is a flowchart of an exemplary method for forming an array deviceand an array interconnect layer, according to some embodiments.

FIG. 8 is a flowchart of an exemplary method for joining an array deviceand a peripheral device, according to some embodiments.

Embodiments of the present disclosure will be described with referenceto the accompanying drawings.

DETAILED DESCRIPTION

Although specific configurations and arrangements are discussed, itshould be understood that this is done for illustrative purposes only. Aperson skilled in the pertinent art will recognize that otherconfigurations and arrangements can be used without departing from thespirit and scope of the present disclosure. It will be apparent to aperson skilled in the pertinent art that the present disclosure can alsobe employed in a variety of other applications.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” “some embodiments,” etc.,indicate that the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases do not necessarily refer to the same embodiment. Further,when a particular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of aperson skilled in the pertinent art to effect such feature, structure orcharacteristic in connection with other embodiments whether or notexplicitly described.

In general, terminology may be understood at least in part from usage incontext. For example, the term “one or more” as used herein, dependingat least in part upon context, may be used to describe any feature,structure, or characteristic in a singular sense or may be used todescribe combinations of features, structures or characteristics in aplural sense. Similarly, terms, such as “a,” “an,” or “the,” again, maybe understood to convey a singular usage or to convey a plural usage,depending at least in part upon context.

It should be readily understood that the meaning of “on,” “above,” and“over” in the present disclosure should be interpreted in the broadestmanner such that “on” not only means “directly on” something but alsoincludes the meaning of “on” something with an intermediate feature or alayer therebetween, and that “above” or “over” not only means themeaning of “above” or “over” something but can also include the meaningit is “above” or “over” something with no intermediate feature or layertherebetween (i.e., directly on something).

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

As used herein, the term “substrate” refers to a material onto whichsubsequent material layers are added. The substrate itself can bepatterned. Materials added on top of the substrate can be patterned orcan remain unpatterned. Furthermore, the substrate can include a widearray of semiconductor materials, such as silicon, germanium, galliumarsenide, indium phosphide, etc. Alternatively, the substrate can bemade from an electrically non-conductive material, such as a glass, aplastic, or a sapphire wafer.

As used herein, the term “layer” refers to a material portion includinga region with a thickness. A layer can extend over the entirety of anunderlying or overlying structure, or may have an extent less than theextent of an underlying or overlying structure. Further, a layer can bea region of a homogeneous or inhomogeneous continuous structure that hasa thickness less than the thickness of the continuous structure. Forexample, a layer can be located between any pair of horizontal planesbetween, or at, a top surface and a bottom surface of the continuousstructure. A layer can extend horizontally, vertically, and/or along atapered surface. A substrate can be a layer, can include one or morelayers therein, and/or can have one or more layer thereupon, thereabove,and/or therebelow. A layer can include multiple layers. For example, aninterconnect layer can include one or more conductor and contact layers(in which contacts, interconnect lines, and/or vias are formed) and oneor more dielectric layers.

As used herein, the term “nominal/nominally” refers to a desired, ortarget, value of a characteristic or parameter for a component or aprocess operation, set during the design phase of a product or aprocess, together with a range of values above and/or below the desiredvalue. The range of values can be due to slight variations inmanufacturing processes or tolerances. As used herein, the term “about”indicates the value of a given quantity that can vary based on aparticular technology node associated with the subject semiconductordevice. Based on the particular technology node, the term “about” canindicate a value of a given quantity that varies within, for example,10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

As used herein, the term “3D memory device” refers to a semiconductordevice with vertically oriented strings of memory cell transistors(referred to herein as “memory strings,” such as NAND strings) on alaterally-oriented substrate so that the memory strings extend in thevertical direction with respect to the substrate. As used herein, theterm “vertical/vertically” means nominally perpendicular to the lateralsurface of a substrate.

Various embodiments in accordance with the present disclosure provide a3D memory device with smaller die size, higher device density, andimproved performance compared with other 3D memory devices. Byvertically stacking an array device and BEOL interconnect above aperipheral device, the density of 3D memory devices can be increased.Moreover, by decoupling the peripheral device processing and the arraydevice processing, the thermal budget associated with processing thearray device is not limited by the peripheral device performancerequirement; similarly, the peripheral device performance is notimpacted by the array device processing. For example, the peripheraldevice and the array device can be separately fabricated on differentsubstrates so that certain high-temperature processes for fabricatingthe array device will not adversely affect the fabrication of theperipheral device (e.g., avoid excess diffusion of the dopants, controlthe doping concentration and/or thickness of ion implantation, etc.).

FIG. 1 illustrates a cross-section of an exemplary 3D memory device 100.3D memory device 100 includes a substrate 102 and peripheral devices onsubstrate 102. An interconnect layer 104 for the peripheral devices isformed above substrate 102. A memory array structure 106 is formed aboveinterconnect layer 104.

3D memory device 100 represents an example of a monolithic 3D memorydevice. The term “monolithic” means that the components of the 3D memorydevice are formed on a single substrate. For monolithic 3D memorydevices, the fabrication encounters additional restrictions due to theconvolution of the peripheral device processing and the memory arrayprocessing. For example, the fabrication of memory array structure(e.g., NAND strings) is constrained by the thermal budget associatedwith the peripheral devices that have been formed or to be formed on thesame substrate. In contrast, as described in detail in the presentdisclosure, components of a 3D memory device (e.g., peripheral devicesand memory array structure) can be formed separately on differentsubstrates and then joined to form a non-monolithic 3D memory device.The de-convolution of the peripheral device processing and memory arrayprocessing from each other can improve the performance of the resulting3D memory device.

Further, memory array structure 106 of 3D memory device 100 includes anarray common source for the NAND strings. For example, a polycrystallinesilicon (polysilicon) layer is formed on interconnect layer 104 by, forexample, physical vapor deposition (PVD) or chemical vapor deposition(CVD). A doped region in the polysilicon layer is formed as the arraycommon source by, for example, ion implantation or diffusion. Becausethe mobility of the charge carriers in polysilicon is lower than that insingle crystalline silicon, performance of memory array structure 106 of3D memory device 100 can be reduced. In contrast, as described in detailin the present disclosure, a single crystalline silicon layer can beformed by thinning a silicon substrate and can be used for forming thearray common source for the NAND strings of the 3D memory device,thereby improving the performance of the 3D memory device, according tosome embodiments of the present disclosure.

FIG. 2 illustrates a cross-section of an exemplary 3D memory device 200according to some embodiments of the present disclosure. 3D memorydevice 200 can include a substrate 202, which can include silicon (e.g.,single crystalline silicon), silicon germanium (SiGe), gallium arsenide(GaAs), germanium (Ge), silicon on insulator (SOI) or any other suitablematerials.

3D memory device 200 can include a peripheral device on substrate 202.The peripheral device can be formed “on” substrate 202, in which theentirety or part of the peripheral device is formed in substrate 202(e.g., below the top surface of substrate 202) and/or directly onsubstrate 202. The peripheral device can include a plurality oftransistors 206 formed on substrate 202. An isolation region 204 and adoped region 208 (e.g., a source region or a drain region of transistor206) can be formed in substrate 202 as well.

In some embodiments, the peripheral device can include any suitabledigital, analog, and/or mixed-signal peripheral circuits used forfacilitating the operation of 3D memory device 200. For example, theperipheral device can include one or more of a page buffer, a decoder(e.g., a row decoder and a column decoder), a sense amplifier, a driver,a charge pump, a current or voltage reference, or any active or passivecomponents of the circuits (e.g., transistors, diodes, resistors, orcapacitors). In some embodiments, the peripheral device is formed onsubstrate 202 using complementary metal-oxide-semiconductor (CMOS)technology (also known as a “CMOS chip”).

3D memory device 200 can include a peripheral interconnect layer 222above transistors 206 to transfer electrical signals to and fromtransistors 206. Peripheral interconnect layer 222 can include one ormore contacts, such as a contact 207 and a contact 214, and one or moreinterconnect conductor layers, such as a conductor layer 216 and aconductor layer 220, each including one or more interconnect linesand/or vias. As used herein, the term “contact” can broadly include anysuitable types of interconnects, such as middle-end-of-line (MEOL)interconnects and back-end-of-line (BEOL) interconnects, includingvertical interconnect accesses (e.g., vias) and lateral lines (e.g.,interconnect lines). Peripheral interconnect layer 222 can furtherinclude one or more interlayer dielectric (ILD) layers, such asdielectric layers 210, 212, and 218. That is, peripheral interconnectlayer 222 can include conductor layers 216 and 220 and dielectric layers210, 212, and 218. The contacts and the conductor layers in peripheralinterconnect layer 222 can include conductor materials including, butnot limited to, tungsten (W), cobalt (Co), copper (Cu), aluminum (Al),silicides, or any combination thereof. The dielectric layers inperipheral interconnect layer 222 can include dielectric materialsincluding, but not limited to, silicon oxide, silicon nitride, siliconoxynitride, doped silicon oxide, or any combination thereof.

3D memory device 200 can include a memory array device above theperipheral device. It is noted that x and y axes are added in FIG. 2 tofurther illustrate the spatial relationship of the components in 3Dmemory device 200. Substrate 202 includes two lateral surfaces (e.g., atop surface and a bottom surface) extending laterally in the x-direction(the lateral direction or width direction). As used herein, whether onecomponent (e.g., a layer or a device) is “on,” “above,” or “below”another component (e.g., a layer or a device) of a semiconductor device(e.g., 3D memory device 200) is determined relative to the substrate ofthe semiconductor device (e.g., substrate 202) in the y-direction (thevertical direction or thickness direction) when the substrate ispositioned in the lowest plane of the semiconductor device in they-direction. The same notion for describing spatial relationship isapplied throughout the present disclosure.

In some embodiments, 3D memory device 200 is a NAND Flash memory devicein which memory cells are provided in the form of an array of NANDstrings 230 extending vertically above substrate 202. The array devicecan include a plurality of NAND strings 230 that extend through aplurality of conductor layer 234 and dielectric layer 236 pairs. Theplurality of conductor/dielectric layer pairs are also referred toherein as an “alternating conductor/dielectric stack” 242. Conductorlayers 234 and dielectric layers 236 in alternating conductor/dielectricstack 242 alternate in the vertical direction. In other words, exceptthe ones at the top or bottom of alternating conductor/dielectric stack242, each conductor layer 234 can be adjoined by two dielectric layers236 on both sides, and each dielectric layer 236 can be adjoined by twoconductor layers 234 on both sides. Conductor layers 234 can each havethe same thickness or have different thicknesses. Similarly, dielectriclayers 236 can each have the same thickness or have differentthicknesses. In some embodiments, alternating conductor/dielectric stack242 includes more conductor layers or more dielectric layers withdifferent materials and/or thicknesses than the conductor/dielectriclayer pair. Conductor layers 234 can include conductor materialsincluding, but not limited to, W, Co, Cu, Al, doped silicon, silicides,or any combination thereof. Dielectric layers 236 can include dielectricmaterials including, but not limited to, silicon oxide, silicon nitride,silicon oxynitride, or any combination thereof.

As shown in FIG. 2 , each NAND string 230 can include a semiconductorchannel 228 and a dielectric layer 229 (also known as “memory film”). Insome embodiments, semiconductor channel 228 includes silicon, such asamorphous silicon, polysilicon, or single crystalline silicon. In someembodiments, dielectric layer 229 is a composite layer including atunneling layer, a storage layer (also known as “charge trap/storagelayer”), and a blocking layer. Each NAND string 230 can have a cylindershape (e.g., a pillar shape). Semiconductor channel 228, the tunnelinglayer, the storage layer, and the blocking layer are arranged along adirection from the center toward the outer surface of the pillar in thisorder, according to some embodiments. The tunneling layer can includesilicon oxide, silicon nitride, or any combination thereof. The blockinglayer can include silicon oxide, silicon nitride, high dielectricconstant (high-k) dielectrics, or any combination thereof. The storagelayer can include silicon nitride, silicon oxynitride, silicon, or anycombination thereof. In some embodiments, dielectric layer 229 includesONO dielectrics (e.g., a tunneling layer including silicon oxide, astorage layer including silicon nitride, and a blocking layer includingsilicon oxide).

In some embodiments, NAND strings 230 further include a plurality ofcontrol gates (each being part of a word line) for NAND strings 230.Each conductor layer 234 in alternating conductor/dielectric stack 242can act as a control gate for each memory cell of NAND string 230. Asshown in FIG. 2 , NAND string 230 can include a select gate 238 (e.g., asource select gate) at an upper end of NAND string 230. NAND string 230can also include another select gate 240 (e.g., a drain select gate) ata lower end of NAND string 230. As used herein, the “upper end” of acomponent (e.g., NAND string 230) is the end further away from substrate202 in the y-direction, and the “lower end” of the component (e.g., NANDstring 230) is the end closer to substrate 202 in the y-direction. Asshown in FIG. 2 , for each NAND string 230, source select gate 238 canbe above drain select gate 240. In some embodiments, select gate 238 andselect gate 240 include conductor materials including, but not limitedto, W, Co, Cu, Al, doped silicon, silicides, or any combination thereof.

In some embodiments, 3D memory device 200 includes an epitaxial layer251 on an upper end of semiconductor channel 228 of NAND string 230.Epitaxial layer 251 can include a semiconductor material, such assilicon. Epitaxial layer 251 can be epitaxially grown from asemiconductor layer 244. For example, semiconductor layer 244 can be asingle crystalline silicon layer, and epitaxial layer 251 can be asingle crystalline silicon layer epitaxially grown from the singlecrystalline silicon layer. Semiconductor layer 244 can be un-doped,partially doped (in the thickness direction and/or the width direction),or fully doped by p-type or n-type dopants. For each NAND string 230,epitaxial layer 251 is referred to herein as an “epitaxial plug.”Epitaxial plug 251 at the upper end of each NAND string 230 can contactboth semiconductor channel 228 and a doped region 250 of semiconductorlayer 244. Epitaxial plug 251 can function as the channel of acorresponding select gate 238 at the upper end of NAND string 230. Asshown in FIG. 2 , semiconductor layer 244 can include two lateralsurfaces (e.g., a top surface and a bottom surface). Each NAND string230 is in contact with the bottom surface of semiconductor layer 244,and a BEOL interconnect layer 253 is in contact with the top surface ofsemiconductor layer 244, according to some embodiments.

In some embodiments, the array device further includes a source contact232 that extends vertically through alternating conductor/dielectricstack 242. As shown in FIG. 2 , an upper end of source contact 232 cancontact doped region 250 of semiconductor layer 244 (e.g., an arraycommon source for NAND strings 230). In some embodiments, source contact232 includes conductor materials including, but not limited to, W, Co,Cu, Al, silicides, or any combination thereof.

In some embodiments, the array device further includes one or more wordline contacts 258 in a staircase structure region. Word line contacts258 can extend vertically within a dielectric layer 259. Each word linecontact 258 can have an end (e.g., the upper end) in contact with acorresponding conductor layer 234 in alternating conductor/dielectricstack 242 to individually address a corresponding word line of the arraydevice. In some embodiments, each word line contact 258 is below acorresponding word line 234. Word line contacts 258 can be contact holesand/or contact trenches (e.g., formed by a wet etch process or a dryetch process) filled with a conductor (e.g., W). In some embodiments,filling the contact holes and/or contact trenches includes depositing abarrier layer, an adhesion layer, and/or a seed layer before depositingthe conductor.

In some embodiments, the array device further includes semiconductorlayer 244 on the upper end of each NAND string 230. Semiconductor layer244 can be a thinned substrate on which the array device is formed. Insome embodiments, semiconductor layer 244 includes a single crystallinesilicon, in which semiconductor layer 244 can be referred to as a“single crystalline silicon layer.” In some embodiments, semiconductorlayer 244 can include SiGe, GaAs, Ge, or any other suitable materials.Semiconductor layer 244 can also include doped region 250 (e.g.,functioning as an array common source for NAND strings 230) and anisolation region 246. Isolation region 246 can extend across an entirethickness or part of the thickness of semiconductor layer 244.

In some embodiments, source contact 232 and NAND strings 230 are both incontact with semiconductor layer 244, so that source contact 232 can beelectrically connected to NAND strings 230 when semiconductor layer 244conducts electrical signals (e.g., when the single crystalline siliconlayer forms an inversion layer for conduction.)

In some embodiments, the array device further includes one or morethrough array contacts (TACs) 241 that extend vertically throughalternating conductor/dielectric stack 242. TAC 241 can extend throughthe entirety of alternating conductor/dielectric stack 242, (e.g., allthe conductor/dielectric pairs) and at least part of isolation region246 in semiconductor layer 244. An upper end of TAC 241 can contact acontact in a contact layer 248 above semiconductor layer 244. TAC 241can carry electrical signals from the peripheral device to a BEOLconductor layer 254 and/or a pad layer 256 by the contact in contactlayer 248.

As shown in FIG. 2 , 3D memory device 200 can include an arrayinterconnect layer 223 above and in contact with peripheral interconnectlayer 222. Array interconnect layer 223 can include bit line contacts226, word line vias 257, one or more conductor layers (e.g., a conductorlayer 224), and one or more dielectric layers (e.g., dielectric layers221 and 225). The conductor layers can include conductor materialsincluding, but not limited to, W, Co, Cu, Al, silicides, or anycombination thereof. The dielectric layers can include dielectricmaterials including, but not limited to, silicon oxide, silicon nitride,low-k dielectrics, or any combination thereof.

As shown in FIG. 2 , each bit line contact 226 can contact the lower endof a corresponding NAND string 230 to individually address correspondingNAND string 230. Each word line via 257 can contact the lower end of acorresponding word line contact 258 to individually address acorresponding word line 234 of NAND strings 230.

A bonding interface 219 can be formed between dielectric layer 218 ofperipheral interconnect layer 222 and dielectric layer 221 of arrayinterconnect layer 223. Bonding interface 219 can also be formed betweenconductor layer 224 of array interconnect layer 223 and conductor layer220 of peripheral interconnect layer 222. Each of dielectric layer 218and dielectric layer 221 can include silicon nitride or silicon oxide.

In some embodiments, a first semiconductor structure 260 is bonded to asecond semiconductor structure 262 at bonding interface 219. Firstsemiconductor structure 260 can include substrate 202, one or moreperipheral devices on substrate 202, and peripheral interconnect layer222. Second semiconductor structure 262 can include semiconductor layer244 (e.g., a thinned substrate), array interconnect layer 223,alternating conductor/dielectric stack 242 having a plurality ofconductor/dielectric layer pairs, and NAND strings 230. Firstsemiconductor structure 260 can include the elements shown below bondinginterface 219 in FIG. 2 , while second semiconductor structure 262 caninclude the elements shown above bonding interface 219 in FIG. 2 .Peripheral interconnect layer 222 can include conductor layer 220, whichcontacts conductor layer 224 of array interconnect layer 223 at bondinginterface 219. Peripheral interconnect layer 222 can also includedielectric layer 218, which contacts dielectric layer 221 of arrayinterconnect layer 223 at bonding interface 219.

As shown in FIG. 2 , 3D memory device 200 can further include BEOLinterconnect layer 253 above semiconductor layer 244. In someembodiments, BEOL interconnect layer 253 includes conductor layer 254,contact layer 248, one or more dielectric layers (e.g., a dielectriclayer 252), and one or more pad layers (e.g., pad layer 256). BEOLinterconnect layer 253 can transfer electrical signals between 3D memorydevice 200 and external circuits. The conductor layers, contact layers,and pad layers in BEOL interconnect layer 253 can include conductormaterials including, but not limited to, W, Co, Cu, Al, silicides, orany combination thereof. The dielectric layers in BEOL interconnectlayer 253 can include dielectric materials including, but not limitedto, silicon oxide, silicon nitride, low-k dielectrics, or anycombination thereof.

BEOL interconnect layer 253 can be electrically connected to theperipheral device. Specifically, the contact in contact layer 248 ofBEOL interconnect layer 253 can extend vertically through at least partof dielectric layer 252 and at least part of isolation region 246 ofsemiconductor layer 244 and can contact the upper end of TAC 241. TAC241 can extend vertically through alternating conductor/dielectric stack242. The lower end of TAC 241 can be in contact with a contact in arrayinterconnect layer 223.

FIG. 3A to FIG. 3D illustrate an exemplary fabrication process forforming a peripheral device and a peripheral interconnect layer. FIG. 6is a flowchart of an exemplary method 600 for forming a peripheraldevice and a peripheral interconnect layer. An example of the peripheraldevice and peripheral interconnect layer depicted in FIGS. 3A-3D andFIG. 6 is the peripheral device (e.g., transistors 206) and peripheralinterconnect layer 222 depicted in FIG. 2 . It should be understood thatthe operations shown in method 600 are not exhaustive and that otheroperations can be performed as well before, after, or between any of theillustrated operations.

Referring to FIG. 6 , method 600 starts at operation 602, in which aperipheral device is formed on a first substrate. The first substratecan be a silicon substrate. As illustrated in FIG. 3A, a peripheraldevice is formed on a first silicon substrate 302. The peripheral devicecan include a plurality of transistors 304 formed on first siliconsubstrate 302. Transistors 304 can be formed by a plurality ofprocessing steps including, but not limited to, photolithography,dry/wet etch, thin film deposition, thermal growth, implantation, CMP,or any combination thereof. In some embodiments, doped regions 305 areformed in first silicon substrate 302, which function, for example, assource regions and/or drain regions of transistors 304. In someembodiments, an isolation region 306 is also formed in first siliconsubstrate 302.

Method 600 proceeds to operation 604, as illustrated in FIG. 6 , inwhich one or more dielectric layers and conductor layers are formedabove the peripheral device. As illustrated in FIG. 3B, a firstdielectric layer 310 can be formed on first silicon substrate 302. Firstdielectric layer 310 can include a contact layer 308, including MEOLcontacts, to make electrical connections with the peripheral device(e.g., transistors 304).

As illustrated in FIG. 3C, a second dielectric layer 316 is formed onfirst dielectric layer 310. In some embodiments, second dielectric layer316 is a combination of multiple layers formed in separate steps. Forexample, second dielectric layer 316 can include a conductor layer 312and a contact layer 314. The conductor layers (e.g., conductor layer312) and contact layers (e.g., contact layers 308 and 314) can includeconductor materials deposited by one or more thin film depositionprocesses including, but not limited to, CVD, PVD, ALD, electroplating,electroless plating, or any combination thereof. Fabrication processesto form the conductor layers and contact layers can also includephotolithography, CMP, wet/dry etch, or any combination thereof. Thedielectric layers (e.g., dielectric layers 310 and 316) can includedielectric materials deposited by one or more thin film depositionprocesses including, but not limited to, CVD, PVD, ALD, or anycombination thereof.

Method 600 proceeds to operation 606, as illustrated in FIG. 6 , inwhich a top dielectric layer and a top conductor layer of a peripheralinterconnect layer are formed. The dielectric layers and conductorlayers formed at operations 604 and 606 can be collectively referred toas an “interconnect layer” (e.g., the peripheral interconnect layer).Each of the dielectric layers and conductor layers can be a portion ofthe peripheral interconnect layer that transfers electrical signals toand from the peripheral device. As illustrated in FIG. 3D, a thirddielectric layer (the top dielectric layer) 318 is formed on seconddielectric layer 316, and a top conductor layer 320 is formed in thirddielectric layer 318. As a result, a peripheral interconnect layer 322is formed. The conductor layers (e.g., conductor layer 320) can includeconductor materials deposited by one or more thin film depositionprocesses including, but not limited to, CVD, PVD, ALD, electroplating,electroless plating, or any combination thereof. Fabrication processesto form the conductor layer and contact layers can also includephotolithography, CMP, wet/dry etch, or any combination thereof. Thedielectric layers (e.g., dielectric layer 318) can include dielectricmaterials deposited by one or more thin film deposition processesincluding, but not limited to, CVD, PVD, ALD, or any combinationthereof.

FIG. 4A to FIG. 4D illustrate an exemplary fabrication process forforming an array device and an array interconnect layer. FIG. 7 is aflowchart of an exemplary method 700 for forming an array device and anarray interconnect layer. An example of the array device and arrayinterconnect layer depicted in FIGS. 4A-4D and FIG. 7 is the arraydevice (e.g., NAND strings 230) and the array interconnect layer 223depicted in FIG. 2 . It should be understood that the operations shownin method 700 are not exhaustive and that other operations can beperformed as well before, after, or between any of the illustratedoperations.

Referring to FIG. 7 , method 700 starts at operation 702, in which adoped region and an isolation region are formed on a second substrate.The second substrate can be a silicon substrate, such as a secondsilicon substrate 402 in FIG. 4A. An array device can be formed onsecond silicon substrate 402. In some embodiments, a doped region 404and an isolation region 406 are formed in second silicon substrate 402.Doped region 404 can be formed by ion implantation and/or diffusion.Isolation region 406 can be formed by thermal growth and/or thin filmdeposition. Patterning process (e.g., photolithography and dry/wet etch)can be used for patterning doped region 404 and isolation region 406 insecond silicon substrate 402.

Method 700 proceeds to operation 704, as illustrated in FIG. 7 , inwhich a plurality of dielectric layer pairs (also referred to herein asan “alternating dielectric stack”) are formed on the second substrate.As illustrated in FIG. 4B, a plurality of dielectric layer 410 anddielectric layer 412 layer pairs are formed on second silicon substrate402. The plurality of dielectric pairs can form an alternatingdielectric stack 408. Alternating dielectric stack 408 can include analternating stack of a first dielectric layer 410 and a seconddielectric layer 412 that is different from first dielectric layer 410.In some embodiments, each dielectric layer pair includes a layer ofsilicon nitride and a layer of silicon oxide. In some embodiments, thereare more layers than the dielectric layer pairs made of differentmaterials and with different thicknesses in alternating dielectric stack408. Alternating dielectric stack 408 can be formed by one or more thinfilm deposition processes including, but not limited to, CVD, PVD, ALD,or any combination thereof. In some embodiments, alternating dielectricstack 408 can be replaced by a plurality of conductor/dielectric layerpairs, i.e., an alternating stack of a conductor layer (e.g.,polysilicon) and a dielectric layer (e.g., silicon oxide).

Method 700 proceeds to operation 706, as illustrated in FIG. 7 , inwhich a plurality of NAND strings of the array device are formed on thesecond substrate. As illustrated in FIG. 4C, a plurality of NAND strings418 are formed on second silicon substrate 402. Each dielectric layer410 of alternating dielectric stack 408 can be replaced by a conductorlayer 416, thereby forming a plurality of conductor/dielectric layerpairs in an alternating conductor/dielectric stack 414. The replacementof dielectric layers 410 with conductor layers 416 can be performed bywet etching dielectric layers 410 selective to dielectric layers 412 andfilling the structure with conductor layers 416. Conductor layers 416can be filled by CVD, ALD, any other suitable process, or anycombination thereof. Conductor layers 416 can include conductormaterials including, but not limited to, W, Co, Cu, Al, polysilicon,silicides, or any combination thereof.

In some embodiments, fabrication processes to form NAND strings 418further include forming a semiconductor channel 420 that extendsvertically through alternating conductor/dielectric stack 414. In someembodiments, fabrication processes to form NAND strings 418 furtherinclude forming a dielectric layer 422 between semiconductor channel 420and the plurality of conductor/dielectric layer pairs in alternatingconductor/dielectric stack 414. Dielectric layer 422 can be a compositedielectric layer, such as a combination of multiple dielectric layersincluding, but not limited to, a tunneling layer, a storage layer, and ablocking layer. The tunneling layer can include dielectric materialsincluding, but not limited to, silicon oxide, silicon nitride, siliconoxynitride, or any combination thereof. The storage layer can includematerials for storing charge for memory operation. The storage layermaterials include, but are not limited to, silicon nitride, siliconoxynitride, a combination of silicon oxide and silicon nitride, or anycombination thereof. The blocking layer can include dielectric materialsincluding, but not limited to, silicon oxide or a combination of siliconoxide/silicon nitride/silicon oxide (ONO). The blocking layer canfurther include a high-k dielectric layer (e.g., aluminum oxide).Dielectric layer 422 can be formed by processes such as ALD, CVD, PVD,any other suitable processes, or any combination thereof.

In some embodiments, fabrication processes to form NAND strings 418further include forming an epitaxial layer 426 at an end of NAND string418. As illustrated in FIG. 4C, epitaxial layer 426 can be formed at alower end of each NAND string 418 as an epitaxial plug 426. Epitaxiallayer 426 can be a silicon layer in contact with and epitaxially grownfrom second silicon substrate 402 and can be implanted to a desireddoping level.

In some embodiments, operation 706 further includes forming one or moresource contacts. As illustrated in FIG. 4C, a source contact 424 thatextends vertically through alternating conductor/dielectric stack 414can be formed on second silicon substrate 402. Source contact 424 canhave an end in contact with doped region 404 of second silicon substrate402. In some embodiments, source contact 424 is electrically connectedto NAND strings 418 by doped region 404 of second silicon substrate 402.A select gate 428 (e.g., a source select gate) can be formed at an endof NAND strings 418 to turn on or turn off doped region 404 of secondsilicon substrate 402 and control a conduction between source contact424 and NAND strings 418. Source contact 424 can include conductormaterials including, but not limited to, W, Co, Cu, Al, doped silicon,silicides, or any combination thereof. Source contact 424 can be formedby a dry/wet etch process to form a vertical opening through alternatingconductor/dielectric stack 414, followed by a fill process to fill theopening with conductor materials and other materials (e.g., dielectricmaterials.) The opening can be filled by ALD, CVD, PVD, electroplating,any other suitable processes, or any combination thereof.

In some embodiments, operation 706 further includes forming one or moreTACs. As illustrated in FIG. 4C, a TAC 431 is formed on second siliconsubstrate 402. TAC 431 can extend vertically through alternatingconductor/dielectric stack 414. In some embodiments, an end of TAC 431is formed in isolation region 406 of second silicon substrate 402. Insome embodiments, fabrication processes to form TAC 431 include forminga vertical opening through alternating conductor/dielectric stack 414 bydry/wet etch process, followed by filling the opening with conductormaterials and other materials (e.g., dielectric material 433) forisolation purposes. TAC 431 can include conductor materials including,but not limited to, W, Co, Cu, Al, doped silicon, silicides, or anycombination thereof. The opening of TAC 431 can be filled with conductormaterials and other materials by ALD, CVD, PVD, electroplating, anyother suitable processes, or any combination thereof.

In some embodiments, operation 706 further includes forming one or moreword line contacts. As illustrated in FIG. 4C, word line contacts 425are formed on second silicon substrate 402. Each word line contact 425can extend vertically through a dielectric layer 423. In someembodiments, an end of word line contact 425 lands on a word line ofNAND strings 418 (e.g., a conductor layer 416), such that each word linecontact 425 is electrically connected to a corresponding conductor layer416. Each word line contact 425 can be electrically connected to acorresponding conductor layer 416 to individually address acorresponding word line of NAND strings 418. One or more word linecontacts 425 can further land on second silicon substrate 402 or selectgates of NAND strings 418 (e.g., source select gate 428 or a drainselect gate 430).

In some embodiments, fabrication processes to form word line contacts425 include forming a vertical opening through dielectric layer 423using dry/wet etch process, followed by filling the opening withconductor materials and other materials (e.g., a barrier layer, anadhesion layer, and/or a seed layer) for conductor filling, adhesion,and/or other purposes. Word line contacts 425 can include conductormaterials including, but not limited to, W, Co, Cu, Al, doped silicon,silicides, or any combination thereof. The openings of word linecontacts 425 can be filled with conductor materials and other materialsby ALD, CVD, PVD, electroplating, any other suitable processes, or anycombination thereof.

Method 700 proceeds to operation 708, as illustrated in FIG. 7 , inwhich an array interconnect layer is formed above the plurality of NANDstrings. The array interconnect layer can transfer electrical signalsbetween the NAND strings and other parts of the 3D memory devices, suchas the peripheral device. As illustrated in FIG. 4D, an arrayinterconnect layer 438 is formed above NAND strings 418. In someembodiments, fabrication processes to form array interconnect layer 438include forming a dielectric layer 434, followed by forming a pluralityof bit line contacts 432 in contact with NAND strings 418 in dielectriclayer 434. Dielectric layer 434 can include one or more layers ofdielectric materials such as silicon oxide, silicon nitride, siliconoxynitride, or any combination thereof. Bit line contacts 432 can beformed by forming openings in dielectric layer 434, followed by fillingthe openings with conductor materials and dielectric materials. Bit linecontact 432 can include conductor materials including, but not limitedto, W, Co, Cu, Al, doped silicon, silicides, or any combination thereof.The openings of bit line contact 432 can be filled with conductormaterials and dielectric materials by ALD, CVD, PVD, any other suitableprocesses, or any combination thereof.

In some embodiments, fabrication processes to form array interconnectlayer 438 further include forming a plurality of word line vias 437 indielectric layer 434. Each word line via 437 can contact an end of acorresponding word line contact 425 to enable electrical connections.Word line vias 437 can be formed by forming openings in dielectric layer434, followed by filling the openings with conductor materials. Othermaterials, such as barrier materials and/or seed layer materials, canalso be used to partially fill the openings before filling the conductormaterials to enhance the adhesion or filling performance of theconductor materials. Word line vias 437 can include conductor materialsincluding, but not limited to, W, Co, Cu, Al, doped silicon, silicides,or any combination thereof. The openings of word line vias 437 can befilled with conductor materials and barrier materials by ALD, CVD, PVD,electroplating, any other suitable processes, or any combinationthereof.

In some embodiments, fabrication processes to form array interconnectlayer 438 further include forming one or more conductor layers (e.g., aconductor layer 440) and one or more contact layer 444 in dielectriclayer 434. Conductor layer 440 and contact layer 444 can includeconductor materials including, but not limited to, W, Co, Cu, Al, dopedsilicon, silicides, or any combination thereof. Conductor layers 440 andconductor contact layers 444 can be formed by any suitable known BEOLmethods.

In some embodiments, fabrication processes to form array interconnectlayer 438 further include forming a top conductor layer 442 and a topdielectric layer 436. Top conductor layer 442 can include conductormaterials including, but not limited to, W, Co, Cu, Al, doped silicon,silicides, or any combination thereof. Dielectric layer 436 can includedielectric materials including, but not limited to, silicon oxide,silicon nitride, silicon oxynitride, or any combination thereof.

FIG. 5A to FIG. 5C illustrate an exemplary fabrication process forforming a 3D memory device with the array device and peripheral device.FIG. 8 is a flowchart for an exemplary method 800 of joining the arraydevice and the peripheral device. An example of the 3D memory devicedepicted in FIGS. 5A-5C and FIG. 8 is 3D memory device 200 described inFIG. 2 . It should be understood that the operations shown in method 800are not exhaustive and that other operations can be performed as wellbefore, after, or between any of the illustrated operations.

Referring to FIG. 8 , method 800 starts at operation 802, in which thearray device (and the array interconnect layer) is positioned below thesecond substrate (e.g., by flipping the second substrate upside down),and the array interconnect layer is aligned with the peripheralinterconnect layer. As illustrated in FIG. 5A, array interconnect layer438 can be placed below second silicon substrate 402. In someembodiments, aligning array interconnect layer 438 with peripheralinterconnect layer 322 is performed by aligning conductor layer 442 ofarray interconnect layer 438 with conductor layer 320 of peripheralinterconnect layer 322. As a result, conductor layer 442 can contactconductor layer 320 when the array device is joined with the peripheraldevice.

Method 800 proceeds to operation 804, as illustrated in FIG. 8 , inwhich the array interconnect layer is joined with the peripheralinterconnect layer. The array interconnect layer can be joined with theperipheral interconnect layer by flip-chip bonding the first and secondsubstrates. In some embodiments, the array interconnect layer and theperipheral interconnect layer are joined by hybrid bonding of the firstsubstrate and the second substrate in a face-to-face manner, such thatthe array interconnect layer is above and in contact with the peripheralinterconnect layer in the resulting 3D memory device. Hybrid bonding(also known as “metal/dielectric hybrid bonding”) can be a directbonding technology (e.g., forming bonding between surfaces without usingintermediate layers, such as solder or adhesives), which obtainsmetal-metal bonding and dielectric-dielectric bonding simultaneously. Asillustrated in FIG. 5B, array interconnect layer 438 can be joined withperipheral interconnect layer 322, thereby forming a bonding interface503.

As illustrated in FIG. 5A, a treatment process 502 can be used toenhance the bonding strength between array interconnect layer 438 andperipheral interconnect layer 322 before or during the joining processof the two interconnect layers. In some embodiments, each of dielectriclayer 436 and dielectric layer 318 includes silicon oxide or siliconnitride. In some embodiments, treatment process 502 includes a plasmatreatment that treats the surfaces of array interconnect layer 438 andperipheral interconnect layer 322 so that the surfaces of the twointerconnect layers form chemical bonds between dielectric layer 436 anddielectric layer 318. In some embodiments, treatment process 502includes a wet process that treats the surfaces of array interconnectlayer 438 and peripheral interconnect layer 322 so that the surfaces ofthe two interconnect layers form preferable chemical bonds to enhancethe bonding strength between two dielectric layers 436 and 318. In someembodiments, treatment process 502 includes a thermal process that canbe performed at a temperature from about 250° C. to about 600° C. (e.g.,from 250° C. to 600° C.). The thermal process can cause inter-diffusionbetween conductor layer 442 and conductor layer 320. As a result,conductor layer 442 can be inter-mixed with conductor layer 320 afterthe joining process. Conductor layer 442 and conductor layer 320 caneach includes Cu.

Method 800 proceeds to operation 806, as illustrated in FIG. 8 , inwhich the second substrate is thinned so that the thinned secondsubstrate serves as a semiconductor layer above the array device (e.g.,the NAND strings). As illustrated in FIG. 5B, the thinned second siliconsubstrate 402 can be a single crystalline silicon layer 504. In someembodiments, after the thinning process, single crystalline siliconlayer 504 has a thickness between about 200 nm and about 5 μm, such asbetween 200 nm and 5 μm (e.g., 200 nm, 300 nm, 400 nm, 500 nm, 600 nm,700 nm, 800 nm, 900 nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, any range boundedon the lower end by any of these values, or in any range defined by anytwo of these values). In some embodiments, single crystalline siliconlayer 504 has a thickness between about 150 nm and about 50 μm, such asbetween 150 nm and 50 μm (e.g., 150 nm, 200 nm, 300 nm, 400 nm, 500 nm,1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50μm, any range bounded on the lower end by any of these values, or in anyrange defined by any two of these values). In some embodiments, singlecrystalline silicon layer 504 has a thickness between about 500 nm andabout 10 μm, such as between 500 nm and 10 μm (e.g., 500 nm, 600 nm, 700nm, 800 nm, 900 nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9μm, 10 μm, any range bounded on the lower end by any of these values, orin any range defined by any two of these values). In some embodiments,single crystalline silicon layer 504 has a thickness less than about 1μm, such as less than 1 μm (e.g., 1 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 150 nm, 200 nm, 300 nm,400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, any range bounded on thelower end by any of these values, or in any range defined by any two ofthese values). Second substrate 402 can be thinned by processesincluding, but not limited to, wafer grinding, dry etch, wet etch, CMP,any other suitable processes, or any combination thereof.

Method 800 proceeds to operation 808, as illustrated in FIG. 8 , inwhich a BEOL interconnect layer is formed above the semiconductor layer.As illustrated in FIG. 5C, a BEOL interconnect layer 505 is formed abovesingle crystalline silicon layer 504. BEOL interconnect layer 505 caninclude a dielectric layer 506, one or more contact layers 508, one ormore conductor layers 510, and a pad layer 512. Dielectric layer 506 canbe a combination of multiple dielectric layers formed at separateprocess steps. Contact layer 508, conductor layer 510, and pad layer 512can include conductor materials including, but not limited to, W, Co,Cu, Al, doped silicon, silicides, or any combination thereof. Dielectriclayer 506 can include dielectric materials including, but not limitedto, silicon oxide, silicon nitride, silicon oxynitride, low-kdielectrics, or any combination thereof. In some embodiments, pad layer512 is electrically connected to external circuits or devices totransfer electrical signals between the joined array/peripheral deviceand the external circuits or devices.

Various embodiments in accordance with the present disclosure provide a3D memory device with smaller die size, higher device density, andimproved performance compared with other 3D memory devices. Byvertically stacking an array device and BEOL interconnect above aperipheral device, the density of 3D memory devices can be increased.Moreover, by decoupling the peripheral device processing and the arraydevice processing, the thermal budget associated with processing thearray device is not limited by the peripheral device performancerequirement; similarly, the peripheral device performance is notimpacted by the array device processing. For example, the peripheraldevice and the array device can be separately fabricated on differentsubstrates so that certain high-temperature processes for fabricatingthe array device will not adversely affect the fabrication of theperipheral device (e.g., avoid excess diffusion of the dopants, controlthe doping concentration and/or thickness of ion implantation, etc.).

In some embodiments, a NAND memory device includes a substrate, one ormore peripheral devices on the substrate, a plurality of NAND stringsabove the one or more peripheral devices, a single crystalline siliconlayer above and in contact with the plurality of NAND strings, and oneor more first interconnect layers formed between the one or moreperipheral devices and the plurality of NAND strings.

In some embodiments, a NAND memory device includes a substrate, analternating conductor/dielectric stack on the substrate, a plurality ofNAND strings, and a single crystalline silicon layer above and incontact with the plurality of NAND strings. Each of the plurality ofNAND strings includes a semiconductor channel extending verticallythrough the alternating conductor/dielectric stack, a tunneling layerbetween the alternating conductor/dielectric stack and the semiconductorchannel, and a storage layer between the tunneling layer and thealternating conductor/dielectric stack.

In some embodiments, a 3D memory device includes a substrate, aperipheral device on the substrate, a memory string extending verticallyabove the peripheral device, a semiconductor layer above the memorystring and in contact with a bottom surface of the semiconductor layer,and a first interconnect layer on a top surface of the semiconductorlayer.

In some embodiments, a 3D memory device includes a substrate, aperipheral device on the substrate, an alternating conductor/dielectricstack above the peripheral device, and a plurality of memory stringsextending vertically through the alternating conductor/dielectric stack.Each of the memory strings includes a semiconductor channel extendingvertically through the alternating conductor/dielectric stack, atunneling layer between the alternating conductor/dielectric stack andthe semiconductor channel, a storage layer between the tunneling layerand the alternating conductor/dielectric stack, and an epitaxialsemiconductor plug at an upper end of the memory string and in contactwith the semiconductor channel.

In some embodiments, a NAND memory device includes a first semiconductorstructure, a second semiconductor structure, and a bonding interfacebetween the first semiconductor structure and the second semiconductorstructure. The first semiconductor structure includes a first substrate,one or more peripheral devices on the first substrate, and a firstinterconnect layer including a first conductor layer at a surface of thefirst interconnect layer. The second semiconductor structure includes athinned second substrate, a plurality of conductor/dielectric layerpairs below the thinned second substrate, a plurality of NAND stringsextending vertically through the plurality of conductor/dielectric layerpairs, and a second interconnect layer including a second conductorlayer at a surface of the second interconnect layer. The first conductorlayer contacts the second conductor layer at the bonding interface.

In some embodiments, a method for forming a NAND memory device isdisclosed. One or more peripheral devices are formed on a firstsubstrate. A plurality of NAND strings are formed on a second substrate.The plurality of NAND strings are positioned above the one or moreperipheral devices. The second substrate is above the plurality of NANDstrings. The plurality of NAND strings and the one or more peripheraldevices are joined. The second substrate is thinned so that the thinnedsecond substrate serves as a single crystalline silicon layer above theplurality of NAND strings.

In some embodiments, a method for forming a 3D memory device isdisclosed. An alternating conductor/dielectric stack and a plurality ofmemory strings extending vertically through the alternatingconductor/dielectric stack are formed on a first substrate. A firstinterconnect layer is formed above the memory strings on the firstsubstrate. A peripheral device is formed on a second substrate. A secondinterconnect layer is formed above the peripheral device on the secondsubstrate. The first substrate and the second substrate are bonded, sothat the first interconnect layer is above and in contact with thesecond interconnect layer.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the present disclosure that others can, byapplying knowledge within the skill of the art, readily modify and/oradapt for various applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent disclosure. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

Embodiments of the present disclosure have been described above with theaid of functional building blocks illustrating the implementation ofspecified functions and relationships thereof. The boundaries of thesefunctional building blocks have been arbitrarily defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed.

The Summary and Abstract sections may set forth one or more but not allexemplary embodiments of the present disclosure as contemplated by theinventor(s), and thus, are not intended to limit the present disclosureand the appended claims in any way.

The breadth and scope of the present disclosure should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

What is claimed is:
 1. A method for forming a NAND memory device,comprising: forming one or more peripheral devices on a first substrate;forming a plurality of NAND strings on a second substrate that is asingle crystalline semiconductor substrate; positioning the plurality ofNAND strings above the one or more peripheral devices, wherein thesecond substrate is above the plurality of NAND strings; joining theplurality of NAND strings and the one or more peripheral devices;thinning the second substrate, so that a remaining portion of the secondsubstrate forms a single crystalline silicon layer above the pluralityof NAND strings; and forming a third interconnect layer above the singlecrystalline silicon layer.
 2. The method of claim 1, further comprising:prior to the joining of the plurality of NAND strings and the one ormore peripheral devices, forming a first interconnect layer for the oneor more peripheral devices.
 3. The method of claim 2, furthercomprising: prior to the joining of the plurality of NAND strings andthe one or more peripheral devices, forming a second interconnect layerfor the plurality of NAND strings.
 4. The method of claim 1, wherein thejoining the plurality of NAND strings and the one or more peripheraldevices comprises joining via a thermal treatment.
 5. The method ofclaim 1, wherein the joining the plurality of NAND strings and the oneor more peripheral devices comprises joining via a plasma treatment. 6.The method of claim 1, further comprising: forming an alternatingconductor/dielectric stack on the second substrate.
 7. The method ofclaim 6, wherein forming the plurality of NAND strings comprises forminga semiconductor channel extending vertically through the alternatingconductor/dielectric stack.
 8. The method of claim 7, wherein formingthe plurality of NAND strings further comprises forming an epitaxiallayer in contact with the semiconductor channel and the singlecrystalline silicon layer.
 9. The method of claim 8, wherein forming theplurality of NAND strings further comprises forming an isolation regionand a doped region in the second substrate.
 10. The method of claim 6,further comprising: forming a plurality of contacts that extendvertically, wherein each of the plurality of contacts comprises an endin contact with a conductor layer of the alternatingconductor/dielectric stack.
 11. The method of claim 1, wherein thinningthe second substrate comprises one or more of grinding, dry etching, wetetching, and chemical mechanical polishing (CMP) the second substrate.12. The method of claim 1, wherein joining the plurality of NAND stringsand the one or more peripheral devices comprises forming chemical bondsbetween dielectric materials on the first substrate and the secondsubstrate.
 13. The method of claim 12, wherein joining the plurality ofNAND strings and the one or more peripheral devices further comprisescausing a physical inter-diffusion of conductor materials on the firstsubstrate and the second substrate.
 14. A method for forming athree-dimensional (3D) memory device, comprising: forming a doped regionand an isolation region in a first substrate from a first side; forming,on the doped region, an alternating conductor/dielectric stack; formingmemory strings, a first contact and a third contact extending throughthe alternating conductor/dielectric stack, wherein the third contactand the memory strings contact the doped region and the first contactextends into the isolation region; forming, on the first substrate, afirst interconnect layer above the memory strings; forming a peripheraldevice on a second substrate; forming, on the second substrate, a secondinterconnect layer above the peripheral device; bonding the firstsubstrate and the second substrate, so that the first interconnect layeris above and in contact with the second interconnect layer; and forminga third interconnect layer on a second side of the first substrate thatis opposite to the first side.
 15. The method of claim 14, furthercomprising: after bonding the first substrate and the second substrate,thinning the first substrate to form a single crystalline silicon layer.16. The method of claim 15, wherein the forming of the firstinterconnect layer comprises forming the first interconnect layer incontact with the first contact.
 17. The method of claim 16, furthercomprising: forming, after bonding the first substrate and the secondsubstrate, a second contact extending through at least part of theisolation region and in contact with the first contact so that the thirdinterconnect layer is electrically connected to the first interconnectlayer.
 18. The method of claim 14, wherein bonding the first substrateand the second substrate comprises bonding the first and secondsubstrates by hybrid bonding.
 19. The method of claim 3, furthercomprising: forming contacts to connect the first interconnect layer andthe third interconnect layer.
 20. The method of claim 14, wherein theforming of the first interconnect layer comprises forming the firstinterconnect layer in contact with the third contact and the memorystrings.
 21. The method of claim 17, further comprising: prior toforming the alternating conductor/dielectric stack, forming an isolationregion in the first substrate from the first side; and after forming thealternating conductor/dielectric stack, forming the first contactextending through the alternating conductor/dielectric stack and intothe isolation region.